The present application relates to a bone anchoring device for the dynamic stabilization of bones, in particular for the dynamic stabilization of the spine. The bone anchoring device includes a bone anchoring element which can be connected to a flexible rod being made of an elastic material. For fixation of the rod, an engagement structure is provided which has such a shape that the pressure distribution on the rod in the fixed state is equalized.
EP 1 759 646 A1 discloses a spinal implant for the dynamic stabilization of the spine which uses a flexible rod made of an elastomer material. The rod is fixed in the receiving part by means of a locking device which clamps the rod by frictional forces with indirect form-fit contribution.
EP 1 795 134 A1 discloses a polyaxial screw for use with a flexible rod made of an elastomer material. To fix the rod or hold the rod in place, an engagement structure is provided in the receiving part receiving the rod and on the locking device locking the rod in the receiving part. The engagement structure comprises ribs or grooves which have a symmetric cross section in each sectional plane. The ribs press onto the elastomer rod causing a depression in the surface of the rod, while leaving the surface structure of the rod intact.
In some circumstances, in particular if high tensional loads act onto the rod, it is necessary to apply a high clamping force on the rod via the locking device to fix the rod. In such a case, there might be the risk that local pressure peaks could result in a structural damage with increased abrasion of the surface of the rod caused by the engagement structure. To avoid this, the height of the engagement structure could be reduced.
Based on the above, there is a need for a bone anchoring device which provides a safe fixation of the rod under high load conditions, and in particular, under high tensional load conditions acting onto the rod